Field of the Invention and Description of Related Arts
The present invention broadly relates to an optical endoscope and, more particularly, to a light control device for an endoscope capable of automatically maintaining an adequate level of light intensity regardless of the size of the image frame.
In recent years, endoscopes find spreading use because it enables an affected part of a living body to be observed by an elongated probe or sensing portion which is adapted to be inserted into a body cavity, thus eliminating any surgical operation for cutting out the affected part.
In recent years, soft endoscopes, known also as fiber scopes, have been proposed in which an image guide is constituted by a flexible fiber bundle for easy insertion into curved body cavities.
Fiber scopes of various diameters are available and selectively used according to the objective portions. Therefore, when a video converter is connected to the fiber scope to enable monitoring, the size of the image, i.e., the diameter of the endoscopic image on the monitor, varies depending on the diameter of the fiber scope to which the video converter is connected.
In addition, the level of the light control also is changed according to the diameter of the image guide constituted by the fiber scope.
Since the light intensity level varies according to the diameter of the image guide of the fiber scope bundle, it is necessary to manipulate, for example, a light control switch, in order to set the light intensity at the optimum level. Thus, the light control adjusting operation has to be conducted each time the scopes of different image frame size is used. This is quite troublesome and, if the endoscopic observation has been started without previous adjustment, it is necessary to conduct the adjustment in the course of the inspection, with the result that the inspection is suspended or the inspection time is prolonged, thus adversely affecting the inspection.
Under this circumstance, the specification of the U.S. Pat. No. 4,628,362 discloses an endoscope apparatus in which a window is defined in an image area and the brightness of the monitor image is automatically controlled in accordance with a signal derived from the window.
This known apparatus, however, requires a manual setting when the image guide is changed to one having a different diameter. Thus, the above-described problems still remains unsolved.